Annekatrien,
I am doing my first steps with i.atcorr now.
I have added (with support from Yann Chemin) the specs for
IRS 1C LISS which I need for a project. Also did some manual
cosmetics.
To warm up, I am doing first tests with the North Carolina
test data set [1] which contains sample LANDSAT 7 data
at reduced size.
I observe that the module (or the procedure) is pretty slow,
perhaps 5 pixels/second on my 2.5GHz box... said this, some
comments below:
On Fri, Jan 30, 2009 at 6:01 PM, Annekatrien Debien
<annekatrien.debien@gmail.com> wrote:
Hi all,
I want to do an atmospheric correction of my Landsat ETM+ images using the
i.atcorr module in Grass 6.3 on Ubuntu, but I never get an output.
what does that precisely mean? It keeps you at 0% and calculates or
it exists and no output?
With NC data, I get (I hope I got the icnd.txt file right):
# set region:
g.region rast=lsat7_2002_10 -p
# get central scene LatLong coordinates:
g.region -gb | grep ll_c
ll_clon=-78.70014170
ll_clat=35.71092005
cat icnd.txt
8 - geometrical conditions=Landsat ETM+
5 24 15.50 -78.700 35.710 - month day hh.ddd longitude latitude
("hh.ddd" is a decimal hour GMT)
2 - atmospheric mode=midlatitude summer
1 - aerosols model=continental
50 - visibility [km] (aerosol model concentration)
-.600 - target at 600m above sea level
-1000 - sensor on board a satellite
61 - 1th band of ETM+ Landsat 7
To be sure about the time (Landsat overpass, North Carolina is UTC-5):
http://earthobservatory.nasa.gov/MissionControl/overpass.php
# zoom to be faster for a test
d.zoom
# We can check the sun position with r.sunmask:
r.sunmask -s --v lsat7_2002_10 out=dummy year=2002 \
month=5 day=24 hour=10 minute=30 sec=0 timezone=-5
Using map center coordinates: 636732.750000 217569.000000
Calculating sun position... (using solpos (V. 11 April 2001) from NREL)
2002.05.24, daynum 144, time: 10:30:00 (decimal time: 10.500000)
long: -78.700150, lat: 35.710922, timezone: -5.000000
Solar position: sun azimuth: 117.002434,
sun angle above horz.(refraction corrected): 63.261234
Sunrise time (without refraction): 05:08:34
Sunset time (without refraction): 19:15:46
No map calculation requested. Finished.
# do the correction
i.atcorr lsat7_2002_10 ialt=elevation icnd=icnd.txt \
oimg=lsat7_2002_10_atcorr
* ****************************** 6s version 4.2b
****************************** *
* geometrical conditions identity
*
* -------------------------------
*
* etm+ observation
*
*
*
* month: 5 day: 24
*
* solar zenith angle: 26.71 deg solar azimuthal angle:
117.09 deg *
* view zenith angle: 0.00 deg view azimuthal angle:
0.00 deg *
* scattering angle: 153.29 deg azimuthal angle difference:
117.09 deg *
*
*
* atmospheric model description
*
* -----------------------------
*
* atmospheric model identity :
*
* midlatitude summer (uh2o=2.93g/cm2,uo3=.319cm-atm)
*
*
*
* aerosols type identity :
*
* Continental aerosols model
*
*
*
* optical condition identity :
*
* visibility : 50.00 km opt. thick. 550nm :
0.1518 *
*
*
* spectral condition
*
* ------------------
*
* etm+ 1
*
* value of filter function :
*
* wl inf= 0.435 mic wl sup= 0.520 mic
*
*
*
* target type
*
* -----------
*
* homogeneous ground
*
* constant reflectance over the spectra 0.000
*
*
*
* target elevation description
*
* ----------------------------
*
* ground pressure [mb] 944.86
*
* ground altitude [km] 0.600
*
* gaseous content at target level:
*
* uh2o= 2.189 g/cm2 uo3= 0.317 cm-atm
*
*
*
* atmospheric correction activated
*
* --------------------------------
*
0%
... unfortunately the sun angle differs from the r.sunmask output.
What's wrong?
When I
use a DEM in ialt, the continuous version or the categorized, of the region,
I just get "wavelength less than 0.25 micron let's take
s(1)=s(0.25)". I don't insert an altitude value in my icdn file however,
since I've read that that value would overwrite the DEM. When I do put in an
altitude value, I get a list with the parameters for the 6S-algorithm, and
then 'percent complete', so that seems to be ok, but the algorithm stops
running, so I don't get a corrected image. Does anyone have experience with
this module, and help me with some tips, preferably so I can use my DEM
instead of one altitude value for the whole image?
I have just tried on a tiny subset of lsat7_2002_10_atcorr but I see
that the module uses the *entire* image:
GRASS 6.5.svn (nc_spm_07):~ > g.region -p
projection: 99 (Lambert Conformal Conic)
...
rows: 18
cols: 26
cells: 468
GRASS 6.5.svn (nc_spm_07):~ > fg
i.atcorr lsat7_2002_10 ialt=elevation icnd=icnd.txt
oimg=lsat7_2002_10_atcorr
D0/0: Computed r0, c289
D0/0: Computed r0, c290
D0/0: Computed r0, c291 <- running out of current region!
So some work is still needed.
Markus